a) Field of the Invention
The invention relates to a rinsing tray system for cleaning the pipette tips of multipipettors or the transfer needles of replication systems with pipette tips or transfer needles arranged in the form of a matrix.
b) Description of the Related Art
Multipipettors are used in particular in research carried out on active chemical and biochemical substances in order to test a large number of substances (substance libraries) for their effectiveness for an intended purpose (HTS: high throughput screening). Extremely high throughputs are achieved in particular using multipipettors with pipette tips arranged in the form of a matrix. At the current time, multipipettors of this type with 8xc3x9712=96 and 16xc3x9724=384 pipette tips are in use. By way of example, the commercially available multipipettors produced by Robbins Scientific Sunnyvale, Calif. and OpalJena GmbH (DD Patent 260571) may be mentioned.
In this field, there is a tendency both to have an increasing number of volumes of test substances which are dispensed onto a microtitration plate (MTP) and to minimize the volumes of individual test substances.
While these experiments were previously carried out in MTPs whose wells were arranged in an 8xc3x9712=96 well array, able to accommodate a test substance volume of up to 300 ml per well, formats which employ a multiple of this array (16xc3x9724=384, 32xc3x9748=1536 and 64xc3x9796=6144) are becoming increasingly important. The external dimensions of the MTPs used remain the same, irrespective of the well array, so that proceeding from the-center to-center distance of the wells with the 8xc3x9712 array of 9 mm, the resultant center-to-center distances for the higher formats are 4.5 mm, 2.25 mm and 1.125 mm. The volume which can be introduced into each well is reduced disproportionately.
For some time, there has been increasing use of replication systems, such as for example those supplied by VandP Scientific Inc., CA, to transfer the test substances.
Replication systems comprise a two-dimensional arrangement of transfer needles of identical diameter and are also used to transfer the test substances in HTS applications. In this case, the transfer needles are advantageously designed in such a way that, when they are immersed in a test substance, test substance in the form of a meniscus adheres only to their end side. In this case, the volume of substance which can be transferred is substantially determined by the diameter of the transfer needles used and can be significantly lower than is possible with the above mentioned multipipettors.
A common requirement for both multipipettors and replication systems is that the pipette tips or transfer needles be cleaned after a substance transfer cycle, in order to prevent contamination of the test substance when it is picked up again and to prevent interference with the next cycle and therefore distortion of the results in subsequent cycles.
In the most simple case, the pipette tips are cleaned by taking up clean rinsing liquid from a first vessel and ejecting it into an adjacent second vessel. A first drawback of a solution of this type is that the two vessels have to be alternately arranged beneath the pipette tips, or else the pipette tips have to be guided over the vessels, and a second drawback is that the outer surface of the pipette tips is not sufficiently cleaned by being immersed in the rinsing liquid, which is essentially free from current, and this drawback also leads to contamination of the clean rinsing liquid with test substance.
The first of the above drawbacks is solved using a rinsing tray system for a multipipettor as described in DE 196 35 004 C1. A rinsing tray system of this type comprises a first tray for holding the unused (clean) rinsing liquid and a second tray for holding the contaminated rinsing liquid, the first tray being arranged resting on top of the second tray, and webs with continuous apertures (through-apertures) are distributed over its base at the same grid spacing as a multipipettor in matrix form.
To carry out the rinsing process, the first tray is filled with the clean rinsing liquid via an inlet. To ensure that the filling level in the first tray does not exceed the height of the webs, which would allow it to drain into the second tray via the through-apertures, an overflow or a filling-level sensor is provided. The pipette tips are then immersed in the clean rinsing liquid, filled with this liquid by suction and are emptied again over the through-apertures, so that the rinsing liquid which is contaminated with residues of the test substance which has previously been pipetted passes into the second tray. It is not important whether the relative movement required is carried out by displacement of the rinsing system or of the pipette tips. A rinsing tray system of this nature has a number of significant drawbacks:
Although the pipette tips are cleaned effectively on the inside by repeatedly sucking up and ejecting the rinsing liquid, the outer surface is only wetted by the clean rinsing liquid. Consequently, residues of the previously pipetted test substance contaminates both a fresh batch of test substance and the rinsing liquid when the rinsing process is repeated.
As the trend towards smaller individual test substance volumes increases, the effects of even the tiniest contamination become more dramatic. Although a rinsing system of this type does allow the rinsing liquid in the first tray to be changed completely after each batch, not only does this consume large quantities of rinsing liquid, but also the operation is time-consuming. Therefore, there is still no effective cleaning of the outer surface, and consequently a rinsing tray system of this type appears to be entirely unsuitable for cleaning transfer needles, since these needles pick up the test substance only via their outer surface.
The primary object of the invention is to provide a rinsing tray system for pipette tips or transfer needles which makes it possible to effectively clean pipette tips or transfer needles which are arranged in matrix form without any residues whatsoever and to carry out the rinsing process in a more time-effective manner.
For a rinsing tray system as described above, this object is achieved by the fact that the bottom tray has at least one inlet in order to be continuously filled with rinsing liquid and at least one outlet is present on the top tray.
The rinsing tray system according to the invention does not simply represent a trivial cinematic reversal, since a different arrangement of the means which are known per se results in a completely different action, and therefore a rinsing tray system of this type has features which are different from those known from the prior art. An essential feature of the invention is the continuous filling of the bottom tray with clean rinsing liquid which, in the process, is conveyed via the through-apertures into the top tray and is removed from there. In order to be cleaned, the pipette tips or transfer needles are introduced into the through-apertures. When this takes place, the outer surface of the pipette tips or transfer needles has the clean rinsing liquid flowing around it as a result of the flow generated in the through-apertures, and consequently this surface is cleaned. The residues of test substance which are removed from the surface are conveyed upward in the through-apertures by the flow generated by the continuous feed of clean rinsing liquid and are rinsed over the edge of these apertures.
A decisive advantage over the prior art is that this system reliably avoids the contamination of the container for the clean rinsing liquid which, in a broad sense, includes not only the bottom tray but also the walls surrounding the through-apertures, which project into the top tray as protrusions, as well as the contamination of the clean rinsing liquid located therein. The reliable avoidance of the contamination of the walls surrounding the through-apertures is not only important for preventing contamination of the clean liquid rising up inside these apertures, but also to ensure that, when the pipette tips or transfer needles are reintroduced, when the rinsing process is repeated, these tips or needles are not contaminated again or additionally through contact with the surrounding walls.
Since, in order to be cleaned, the pipette tips or transfer needles are dipped into the through-apertures, the surrounding walls of these apertures, unlike in the prior art, only have to project slightly into the interior of the top tray 1.1, 1.2, forming protrusions of a low height. This leads to the advantageous additional effect that, apart from the required horizontal movement by in each case half the grid spacing in order for the rinsing liquid to be taken up into the through-apertures and released into the top tray, only one vertical movement is required, namely that of lowering the pipette tips or raising the rinsing tray system in order for the tips to be dipped into the through-apertures. Lowering during release of the rinsing liquid is not necessarily required.
A further additional effect consists in the possibility of arranging the through-apertures more closely together and therefore of reducing the grid spacing compared to the prior art, since there is no need for any vent openings. Center-to-center distances of the through-apertures of less than 9 mm, for example of 4.5 mm, 2.25 mm or 1.125 mm, are possible.
There is also no need for an overflow or overflow sensor, which simplifies the construction.
To generate a uniform flow of the rinsing liquid in all the throughapertures, the cross section of these apertures may narrow on the side of the bottom tray in order to restrict the flow.
To ensure that there are no drops formed when the rinsing liquid emerges from the through-apertures and that the continuously conveyed rinsing liquid can flow out, the rim surface around the through-apertures should either be extremely narrow or should form a plane surface which is inclined with respect to the base of the top tray.
To avoid contamination of the rinsing tray system, it is advantageous for those parts which come into contact with the contaminated rinsing liquid and the pipette tips or transfer needles to be made from a suitably hydrophobic material or to be coated with a hydrophobic material.
The invention is to be explained in more detail below with reference to two exemplary embodiments.